1. Field
An embodiment of the invention relates to a device having more than one semiconductor die. More particularly, the embodiment relates to a device having an encapsulated stack of semiconductor dice, and to a method for forming the device.
2. Background
Semiconductor based electronic components of many modern electrical systems are often provided as multiple die packages wherein two or more electrically connected semiconductor die are packaged together. FIG. 1 shows a prior art package 100 containing a stack of separately molded silicon die. The package contains a first substrate 110, a first silicon die 120, a first epoxy molding compound 130 globbed over the first die, a second substrate 150, a second silicon die 160, a second epoxy molding compound 170 globbed over the second die, and solder balls 140 to provide electrical connection between the first and the second silicon die. The second die is stacked over the first die after the molding compounds have been separately globbed over the dice.
Stacked die packages, such as the one shown, offer a number of advantages. One advantage is an ability to separate the functions on each semiconductor die. For example, the first die 120 may contain primarily logic and the second die 160 may contain primarily memory. This separation of functions may simplify fabrication and may improve fabrication yields, inasmuch as the yields of logic die are often less than those of memory die. A further advantage of such packages is that they are compact, have high circuit density, and have low footprint area. This makes these packages particularly useful for providing electronic components and functions for compact electrical systems, such as cellular phones and the like. For these and other reasons, stacked semiconductor dice packages are favored for many modern and commercially significant electronic devices.
Unfortunately, the prior art package 100 and the existing methods for fabricating such a package have a number of disadvantages. One significant disadvantage is that the fabrication method is generally inefficient and contains a number of unnecessary operations. In fabricating the prior art package, each of the die are molded separately to their respective substrates. That is, molding compound 130 is globbed over the first die 120 attached to the first substrate 110, and then, separately, molding compound 170 is globbed over the second die 160 attached to the second substrate 150. Performing these moldings separately often involves either the use of additional/replicate molding equipment, which may increase the manufacturing costs, or else a decrease in manufacturing throughput if the same equipment is used. Additionally, numerous handling operations may need to be performed by operators or machines in order to move the multiple attached die into and out of the molding equipment. Also as a consequence of the separate molding operations, the thickness and regularity of the thickness of the molding compounds 130 and 170 are generally insufficient to allow electrical connection through the solder balls. Accordingly, in the prior art fabrication methods, planarization operations are often used to planarize the top surface of the molding compounds at heights that are similar to the height of the solder balls. Another operation that is often performed in the prior art fabrication method is application of an adhesive to adhere the first molding compound 130 to the second support 150, since the molding compounds are hardened before contact and provide no mechanical connection. Each of these operations may add to the overall cost of packaging the device.
Additionally, even after planarization, the molding compounds often significantly increase the overall thickness of the package. Often, this will not be desired, particularly if the package is to be used in a cellular phone or other small device.